1. Field of the Invention
This invention generally relates to electronic sensors and, more particularly, to a pressure sensitive sensor fabricated using metallic nanoparticles embedded in an elastic polymer medium.
2. Description of the Related Art
Pressure sensors are one of the most common type sensors used today. A pressure sensor acts as a transducer, generating a signal that is a function of the force imposed, to measure strain due to applied pressure over a certain area. Many types of transducers currently exist including piezoresistive, capacitive, electromagnetic, piezoelectric, and optical types. A pressure sensor can also measure change in density of fluid or gas, to gauge environmental pressures. Some examples include pressure sensors designed to measure a change of resonant frequency using micro electromechanical system (MEMS), the thermal change of heated filament, i.e. pirani gauge, or the flow of charged ionic gas particles in cathode gauge.
Recently, display touchscreen pressure sensors have attracted much attention with the driving demand for smart phones, personal data assistants (PDAs), portable game consoles, and tablet personal computers (PCs). Touchscreen revenues are forecast to increase from $3.7B in 2009 to $9.1B by 2015, which is a much faster growth than the display industry overall. Resistive and capacitive types of touchscreen technology have been used for this purpose, but one problem found in all of these technologies is that they are only capable of reporting a single point even when multiple objects are placed on the sensing surface. Projected capacitive touch (PCT) technology allows for multi-touch operations, but it lacks flexibility in that a conductive layer, such as fingertip, is needed as the pointer object. Also, the long-life operation of PCT is limited by conductive smudges that can occur with collective dust that accumulates on the screen as a result of moisture from fingertips.
Another problem in touchscreen technology is the integration issue of “in-cell” touch panels that are built directly into the screen, instead of the conventional “on-cell” approach which requires an additional piece of glass on top of the screen. The “in-cell” touchscreen is attractive because it has the ability to preserve picture quality and maintain the display's original thickness. However, capacitive type sensors tend to create large electromagnetic interference in liquid crystal due to parasitic effects, and the resistive micro-switch type requires high stroke movement, on the order ˜0.5 microns (μm), which can disturb the display operations. Therefore, pressure sensor technologies that can integrate touch panel onto a typical LCD screen with high reliability operations are needed in further advancement of the market.
It would be advantageous if a sensitive pressure sensor could be fabricated that relied upon tunneling current conduction between metallic nanoparticles embedded in an elastic medium to increase sensitivity.